Conditioning of drilling muds



Patented Nov. 3, 1942 CONDITIONING F DRILLING MUDS Jolly W. O'Brien, Houston, Tex.

No Drawing. Refiled for abandoned application Serial No. 257,459, February 20, 1939. This application June 4, 1941, Serial No. 396,579

8 Claims. (Cl. 252-85) The invention relates to a means and method of conditioning drilling muds of the type used in the rotarymethod of drilling wells.

This application is a re-filing of my prior copending application, Serial No. 257,459, filed Feb. 20, 1939 for Conditioning of drilling muds.

1 The requirements of a satisfactory drilling mud are many and varied, depending upon the conditions encountered in the formations, the rate and nature of the drilling, and the pressures and temperatures encountered.

The viscosity and the specific gravity of the drilling mud must be controlled in order to obtain the desired results. If the viscosity becomes too great the friction losses due to circulating the mud'become excessive, the mud must therefore be pumpable. The mud must have a suitable gelling quality which must be sufiicient to carry the cuttings from the well bore, and maintain cuttings in suspension when circulation is suspended, but insuflicient to stick the drill stem, in event circulation is discontinued for a period of time, or to prevent reestablishment of circulation when desired. The specific gravity must be controlled in order to maintain a suflicient pressure on the formation to prevent blowouts. The mud must be sufiiciently thin to prevent gas cutting and to enable the separation of the cuttings from the mud at the surface.

With the foregoing requirements in mind it is one'of the objects of the present invention to provide materials to be admixed with the drilling mud so as to condition it to comply with the foregoing conditions.

Another object of the invention is to provide a finely ground material to be added to the mud which material is composed of strontium sulphate and impurities therein.

Another object of the invention is to add to the drilling mud a finely ground material composed substantially of strontium sulphate along with a viscosity reducin chemical.

Another object of the invention is to add strontium sulphate and dolomite to a drilling mud until the viscosity thereof approaches 40 centipoises (Stormer viscosimeter at 600 R. P. MJ and then adding aviscosity reducing chemical whereby the viscosity is reduced to approximately 20 centipoises and thereafter again adding finely ground strontium sulphate to increase the specific gravity of the drilling mud while maintaining the viscosity below 40 centipoises.

Another object of the invention is to maintain a drillingvmud within the normal range of workable viscosity, namely, between 20 and 40 centipoises while increasing the specific gravity to approximately 14 pounds per gallon by the adding of an impure strontium sulphate and a viscosity reducing chemical.

Another object of the invention is to add to a drilling mud, a solid comprising a finely divided impure strontium sulphate to increase the specific gravity, anda viscosity reducing chemical to decrease the viscosity, wherein the addition of such materials results in an unexpected reduction in viscosity when the proportion of solids added is considered.

Another object of the invention is to add a fienly ground materialwhich is in the nature of a celestite as to its general chemical analysis but which material reacts unexpectedly upon the introduction of a viscosity reducing chemical such as a pyrogenic derivative of phosphoric acid.

Another object of the invention is to reduce the viscosity of the drilling mud to which finely divided solids have been added so that additional solids may thereafter be added to obtain a drilling mud composition approximating 14' pounds per gallon when the viscosity approximates 40 centipoises.

Another object of the invention is to provide a method of maintaining the viscosity of a drilling mud below 40 centipoises while increasing the specific gravity to approximate 1.7 which comprises the adding of an impure strontium sulphate and a viscosity reducing chemical.

Another object of the invention is to produce a drilling mud having the specific gravity approximating 1.7 and a viscosity of less than 40 centipoises by adding to the normal drilling mud a finely divided solid having a specific gravity less than 3.75 and a viscosity reducing chemical.

Other and further objects of the invention will be readily apparent as the detailed description thereof is understood.

An impure strontium sulphate having a chemical analysis substantially as follows, when finely ground, has been found to be satisfactory It will be noted that the principal ingredients of the material when released are strontium oxide."

which the material is to be used. It has been found that in adding the material to an ordinary drilling mud that if a mud having a weight of approximately 9 /2 pounds per gallon with a low viscosity below 10 centipoises'is used as thebase,

that the mere adding of the material results in a mud of approximately, 11 pounds per gallon, weight by the time the viscosity has increased to 40 centipoises due to the addition of the finely divided solid material. Inasmuch as the mud must be readily pumpable it has been found in practice that mud of about 40 centipoises is substantially the maximum viscosity that is satisfactorily serviceable.

the drilling mud in the presence of or whena viscosity reducing chemical is added thereto.

- The discovery of the unexpected results 'due to the admixing of these materials may be due to there-arrangement of the molecular structure of the compounds which could have a decided effect upon the surface characteristics of the particles and thus might account for the excep tional reduction in viscosity, or there may be a upon the conditions and circumstances under chemical reaction between the .materials.

.I Broadly, the invention contemplates the use of a finely divided material having a specific gravity approximating 3.75 which whenadmixed in -a:drilling mud while lowering the viscosity mating 14 poundsrper gallon.

In the event it is desired to either reduce the viscosity and maintain the specific gravity the same or it is desired to reduce the viscosity in order that additional solid matter may be added, then a suitable viscosity reducing chemical can be added ,tothe mud. Some such chemicals are the pyrogenic derivatives of phosphoric acid,

others may be quebracho extract, .gallic acid,

- caustic soda, sodium hexametaphosphate, tetrasodium pyrophosphate or sodium tetraphosphate.

With a mud such as just described, when an amount of chemical ranging from one part in two thousand down to one part in one hundred twenty-five is added, it has been found that the viscosity is reduced from approximately 40 to approximately 20 centipoises. Thus, if a thinner mud is desired the same specific gravity is maintained while reducing the viscosity one-half. While, on the other hand, if it is then desired to have a heavier mud, additional solid matter may be added until the desired Weight is obtained or until the viscosity is again increased due to the addition of such solids to a point approaching the maximumwhich may be used. In event a still heavier mud is then desired, the mud may be again treated with additional viscosity :reducing chemical to again bring down the viscosity so that additional solids may be added, or, as pointed out above, the viscosity may be reduced without the addition of any more solid matter.

It is obvious from the foregoing that satisfactorily serviceable viscosities and specific gravities or combinations of the two may be ob-' .tained and maintained by proportioning the amounts of impure strontium sulphate and viscosity reducing chemicals which are added.

The principal feature of the invention resides A due to the presence of a viscosityreducing chemicalresults in a drilling mud which 5 satisfactorily serviceable and. has a weight What is claimed is:

1. An admix for aqueous drilling mud comprising one part .or less of a viscosity reducing chemical and ninety-nine parts or more ofa material having substantially the following ccmposition:

Silicon dioxide-.. 1.72 Oxides of iron and aluminum 0.08

Calcium oxide-n. 4.32 Magnesium oxide 2.06 Barium oxide 0.84

, chemical in the mud. a 3. An admix for aqueous drilling mud comprising a compound including as its major com- Strontium oxide n- 46.00

Sodium and potassium oxide 0.94 Carbon dioxide 5.62 Sulphur trioxide 35.74 Volatile matter (other than carbon dioxide) 2.73

2. An admix for aqueous drilling mud comprising a compound including as its major component a celestite ore and a proportion of a pyrogenic derivation of phosphoric acid in sufficient quantity to act as a viscosity reducing ponent an impure strontium sulphate containing minor amounts of dolomite and as a minor component a caustic alkali in combination with an inorganic material or acid properties such as sodium acid pyrophosphate in an amount to .serve as a viscosity reducing chemical in the drilling mud.

4. In the art of controlling the specific gravity and viscosity of an aqueous drilling mud used in the rotary method of drilling wells which comprises, adding finely ground celestite to the drilling mud, adding a very slight amount of a viscosity reducing chemical to the mud as the viscosity tends to increase so as to decrease the viscosity below the maximum operating range, and adding additional celestite.

5. A method of maintaining the viscosity of an aqueous drilling mud within the normal operating range between twenty and forty centipoises while increasing the weight from ten to a thirteen and a half pounds per gallon which comprises the steps 'of alternately adding celestite in an amount capableof maintaining such operating range and a viscosity reducing chemical.

6. A method of increasing the specific gravity of an aqueous drilling mud while maintaining the viscositywithin a normal operating range which includes adding celestite and a viscosity reducing chemical.

7. A method of increasing the specific gravity approxi-g creasing the specific gravity to not to exceed 1.7 which comprises adding celestite until the viscosity approaches 40 centipoises, then adding a viscosity reducing chemical to reduce the viscosity, and again adding more celestite.

JOLLY W. O'BRIEN. 

